html,body{
    padding: 0;
    margin: 0;
}
.black{
    position: fixed;
    top:0;
    width: 100vw;
    height: 100vh;
    background: rgba(0,0,0,.6);

}

.white{
    width: 400px;
    height: 200px;
    background: #fff;
    position: absolute;
    top:0;
    bottom: 0;
    left: 0;
    right: 0;
    margin: auto;
}

.btn span{
    width: 100px;
    height: 40px;
    text-align: center;
    line-height: 40px;
    border: 1px solid skyblue;
    color: skyblue;
    margin: 15px;

}